For any geometric sequence, the nth term =
Let's test it with the third term. The third term =
The tenth term is
If you didn't remember the formula, write out the terms, dividing each subsequent term by 4 (which is multiplying it by 1/4), until you reach the 10th term.
64, 64/4=16, 16/4=4, 4/4=1, 1/4=1/4, 1/4 / 4 = 1/16, 1/16 / 4 = 1/64, 1/64 / 4 = 1/256, 1/256/4 = 1/1024, 1/1024 / 4 = 1/4096.